1. Field of the Invention
This invention relates to air diffusers employed in waste water treatment plants, and in particular to an amplitude controlling stop for limiting the opening movements of a leaf spring used to modulate the air outlet ports of such diffusers.
2. Description of the Prior Art
Air diffusion systems employed in sewage treatment aeration tanks generally comprise a plurality of air diffusers supplied by air from headers. These headers are usually disposed in a horizontal position and they are formed with rows of connections to which air diffusers of various designs may be attached.
In recent years, diffusers employing resilient leaf springs which modulate the air from the discharge port openings of the diffuser have found extensive commercial acceptance. The leaf spring designs employed in the prior art are susceptible to easy clogging of the port openings so that reliable diffusion of air in optimum amounts and at all diffuser locations is not attainable. Such clogging is often due to fibrous material becoming lodged between the diffuser body and the leaf spring.
In order to get an adequate amount of air into the aeration tank when clogging occurs, the air pressure is often increased to the point that the leaf springs are forced beyond their elastic limit, resulting in a permanent deformation of the leaf spring. This deformation prevents the leaf spring from completely closing off the diffuser ports. Consequently, sewage water and its sludge clogging contents backup into the diffuser chambers.
As a result of this tendency to deform the leaf springs, the design of leaf spring diffusers has been less than optimum in that the leaf spring bodies are made of materials displaying less resilience than is desirable. The size of the attachment means to the leaf springs body is also excessive. Additionally, because of the restraints on the design and the size of the leaf spring including its attachment to the diffuser body, it is not possible in many instances to design the discharge ports in the diffuser body to deliver minimum pressure drop at the required rates of air delivery to the sewage treatment tank.
U.S. Pat. No. 2,415,048 discloses an air diffuser which employs means for restricting the deflection of a resilient plate. The limiting means shown in that patent is susceptible to excessive clogging and therefore does not disclose a practical solution to the problem of leaf spring deformation.